The present invention relates to heat exchangers that are generally configured comprising a number of internal fluid or gas passages disposed within a surrounding body. In an example embodiment, the internal passages are designed to accommodate passage of a particular fluid or gas in need of cooling, and the body is configured to accommodate passage of a particular cooling fluid or gas used to reduce the temperature of the fluid or gas in the internal passages by heat transfer through the structure of the internal passages. A specific example of such a heat exchanger is one referred to as a shell and tube exchanger, which can be used in such applications as exhaust gas cooling for internal combustion engines, e.g., for use in exhaust gas recirculation systems or the like.
FIG. 1 illustrates a known shell and tube type heat exchanger 10 that is disclosed in U.S. Patent Publication No. 2004/0182547 and that generally includes a tube bundle 12 formed from a number of individual tubes 14, i.e., internal passages, that are aligned together, positioned next to one another, and that have one or both openings at the tube ends 16 positioned adjacent one another. The tube bundle 12 is disposed within a surrounding body or jacket 18. The body is configured having an inlet and outlet (not shown) to facilitate the passage of a cooling medium such as a fluid or gas into and out of the shell.
In the particular embodiment illustrated in FIG. 1, the body or jacket is of a one-piece construction that has enlarged or flared-out end portions 20 that are sized and shaped to extend over tube plates 22 that are disposed within and attached to respective end portions 20, and which tube plates are used to join the tubes together adjacent axial tube ends.
A problem known to exist with such shell and tube type heat exchanges is that the tubes and tube bundle, being subjected to relatively hotter fluids or gasses than that of the heat exchange body or jacket, tends to undergo a degree of thermal expansion that is greater than that of the body or jacket, which if not addressed is known to cause thermal stresses to occur within the heat exchanger that can lead to a mechanical failure, thereby reducing the exchanger service life.
Attempts have been made to address the presence of such unwanted thermal stresses in shell and tube heat exchangers. For example, the heat exchanger illustrated in FIG. 1 has been configured having a body or jacket that includes an expansion bead 24 extending around the body or jacket. In this embodiment, the expansion bead 4 basically comprises a section of the body or jacket that has been deformed outwardly in the form of rounded surface feature that, moving axially along the section, projects outwardly 90 degrees to a rounded closed end that projects inwardly to the body. The expansion bead is designed to permit the body to expand and/or contract as needed to accommodate thermal expansion and/or contraction of the tube bundle disposed therein.
An issue that exists with this design is that the expansion bead, while being configured to address axial-directed thermal expansion of the body, the expansion bead (like the remaining portion of the heat exchanger body) is also subject to vibration loads. To best function as a thermal expansion joint, the expansion bead material thickness should be minimized. However, a thinner material thickness weakens the structural integrity of the heat exchanger and its related ability to carry vibration loads during heat exchanger operation, thereby making such heat exchangers comprising the same subject to mechanical failure and reduced service life.
Additionally, heat exchangers such as that illustrated in FIG. 1 make assembly and/or connection of the tubes and tube plates difficult because at least one of the tube plates have to be attached to the respective tube ends while the tube plate and tube ends are disposed within the end of the body or jacket. The need to attach the tubes to the tube plate while both elements are disposed within the end of the body or jacket increases assembly time and makes accurate leaktight attachment between the tubes and tube plate a challenge.
It is, therefore, desired that a shell and tube heat exchanger be constructed in a manner that addresses the need to accommodate thermal expansion issues that are known to occur in such heat exchangers in a manner that reduces or eliminates thermal stresses from developing therein. It is desired that such construction accommodates the presence of such thermal expansion in a manner that does not otherwise impact the ability of the heat exchanger to carry the vibration loads known to exist for heat exchangers. It is further desired that such heat exchanger construction is configured to facilitate assembly of the heat exchanger elements, such as the tubes and tube plates relative to the heat exchanger body.